The IP Multimedia Subsystem (IMS) is the technology defined by the Third Generation Partnership Project (3GPP) to provide IP multimedia services over mobile communication networks. IP multimedia services can provide a dynamic combination of voice, video, messaging, data, etc. within the same session. The IMS makes use of the Session Initiation Protocol (SIP) to set up and control calls or sessions between user terminals. The Session Description Protocol (SDP), carried by SIP signals, is used to describe and negotiate the media components of the session. Whilst SIP was created as a user-to-user protocol, the IMS allows operators and service providers to control user access to services and to charge users accordingly.
FIG. 1 illustrates schematically how the IMS fits into the mobile network architecture in the case of a General Packet Radio Service (GPRS) access network. As shown in FIG. 1, control of communications occurs at three layers (or planes). The lowest layer is the Connectivity Layer 1, also referred to as the bearer or user plane, and through which signals are directed to/from user equipment (UE) accessing the network. The entities within the connectivity layer 1 that connect an IMS subscriber to IMS services form a network that is referred to as the IP-Connectivity Access Network, IP-CAN. The GPRS network includes various GPRS Support Nodes (GSNs). A Gateway GPRS Support Node (GGSN) 2a acts as an interface between the GPRS backbone network and other networks (radio network and the IMS network). The middle layer is the Control Layer 4, and at the top is the Application Layer 6.
The IMS 3 includes a core network 3a which operates over the Control Layer 4 and the Connectivity Layer 1, and a service network 3b. The IMS core network 3a includes nodes that send/receive signals to/from the GPRS network via the GGSN 2a at the Connectivity Layer 1, as well as network nodes (including Call/Session Control Functions (CSCFs) 5) which operate as SIP proxies within the IMS in the Control Layer 4.
The 3GPP architecture defines three types of CSCFs: the Proxy CSCF (P-CSCF) which is the first point of contact within the IMS for a SIP terminal; the Serving CSCF (S-CSCF) which provides services to the user that the user is subscribed to; and the Interrogating CSCF (I-CSCF) whose role is to identify the correct S-CSCF and to forward to that S-CSCF a request received from a SIP terminal via a P-CSCF. The top, Application Layer 6 includes the IMS service network 3b. Application Servers (ASs) 7 are provided for implementing IMS service functionality.
3GPP specifications (TS 23.228) mandate that every IMS core network subsystem subscriber shall have one or more IMS Private User Identities (IMPI). An IMPI is assigned by the subscriber's home network operator, and is used for IMS registration (i.e. for authorization and authentication purposes). This identity shall take the form of a Network Access Identifier (NAI) as defined in RFC 2486. It should be noted that a subscription may be attached to a person or to an organisation such as a corporation. Nonetheless, in the following discussion the term “user” is used synonymously with the term “Private User Identity”.
A user may have one or more IMS Public User Identities (IMPUs). The Public User Identity/Identities is/are used by any user for requesting communications to other users (in the form of SIP URI—IETF RFC 3261 [26]— or a TEL URL—IETF RFC 3966). The relationship between IMPUs and IMPIs is defined by 3GPP Rel-6 onwards. A user registers a contact address for an IMPU with the IMS core network, using the SIP Register method. This contact address might, for example, be an IP address currently allocated to the user.
In the current IMS operational architecture it is the IMS operator who allocates IMPUs and IMPIs to users, on the basis that there is a business relationship between the users and the IMS network operator. It will of course be appreciated that Users IDs (that is IMPUs and IMPIs) consume resources within the IMS network, primarily within the Home Subscriber Server (HSS) that holds the user profiles; each IMS user has a permanent HSS user profile.
Many companies now provide services via a web site hosted on the Internet. These companies are referred to as Web Service Providers (WSPs), and the service provided by their web site provides is referred to as a third party Internet service.
Many WSPs, such as EBAY™ and GOOGLE™, have their own user subscription databases in order, for example, to allows users to access a premium service (paid or unpaid) once they have signed-up and entered some user-id and password into the WSP user database. Subscribers to a given WSP represent a community of users having some common interest in the service/information supplied by the WSP.
The IMS provides a managed multimedia network with security and QoS capabilities. Whilst the IMS is primarily intended for establishing multimedia sessions between users, it may also be used to establish sessions between network servers and users. This makes IMS networks potentially valuable to WSPs, where the IMS network is exposed to the WSPs via some HTTP interface such as REST or SOAP. In particular, the IMS network can add value to the third party Internet service by allowing web content to be delivered to users via the IMS network, or by allowing users of a third party Internet service community to communicate/interact with each other using the real-time capabilities of the IMS network. For example, a department store web site or an e-commerce web-site may wish to push product information to users, and users may wish to discuss products using real-time multimedia communications. According to this approach, the WSP does not have to invest in (an IMS or other) communications infrastructure, and does not have to manage allocation of IMS IDs.
It is desirable to be able to facilitate such IMS-based communication sessions without overburdening the IMS networks. FIG. 2 illustrates schematically a set of WSPs interacting with an IMS network in order to provide IMS services to their respective user groups.